LCD with diffuser having diffusing particles therein located between polarizers

ABSTRACT

A liquid crystal display includes a patternable diffusing layer therein positioned between the display&#39;s substrates. The diffusing (or diffuser) layer includes a host material having a plurality of particles (e.g. substantially transparent spherical balls or spacers) provided therein in order to perform a diffusion function. The refractive index n p  of the particles is different (i.e. Δn) from the refractive index n h  of the host material by at least about 0.05, and Δn is preferably from about 0.05-0.15. In certain embodiments, photoimageable color filters, with diffusing particles embedded therein, function as discrete diffusing members across the passive substrate. In other embodiments, a substantially continuous diffusing layer with a transparent host, including spherical balls embedded therein, may be provided across the passive substrate between the substrate and the color filters. Still further, the diffusing layer with transparent host material may be provided between the common electrode and black matrix members on the passive substrate.

This invention relates to a liquid crystal display. More particularly,this invention relates to a liquid crystal display (LCD) including adiffuser provided therein at a location between the polarizers.

BACKGROUND OF THE INVENTION

Transflective liquid crystal displays (LCDs) utilize some ambient lightto illuminate active matrix pixels when operating in bright lightenvironments (i.e. high ambient light environments). The direction ofthe ambient light's specular component requires diffusion orrandomization to prevent mirror images off of the surroundings and toenlarge the useful illumination cone. Certain prior art transflectivedisplays have utilized a diffusing layer disposed outside of thedisplay's polarizers (i.e. not between the polarizers and not betweenthe substrates). Strong depolarizing effects and large thicknesses ofconventional diffusers have forced such placement outside of thesubstrates and outside of the polarizers.

For example, see prior art FIG. 1 which is taken from commonly ownedU.S. Pat. No. 5,629,784. As illustrated, the FIG. 1 display includesfrom the rear forward linear polarizer 1, transparent substrate 3,discrete pixel electrodes 7, rear orientation or buffing film 9, liquidcrystal (LC) layer 11, front orientation or buffing film 13, commonelectrode 15, front substrate 17, front linear polarizer 19, opticalfilm 21 including facets 23, holographic diffuser 25, and finally glasssheet 27. It is noted that diffuser 25 is located on the front side ofthe LC layer and outside of the polarizers 1, 19, and also outside (i.e.exterior) of the display's substrates 3, 17. Liquid crystal layer 11,electrodes 7, 15, and orientation films 9, 13 are located between thesubstrates, and between the polarizers.

Unfortunately, prior art diffusing layers, including that of the '784patent shown in FIG. 1 herein, suffer from at least the followingproblems: (i) substantial depolarization of light, (ii) image parallax,and (iii) production problems which prevent practical use between adisplay's substrates.

With regard to depolarization shortcomings of prior art diffusinglayers, such diffusers utilize scattering of input light rays to diffuseor randomize the direction of the output light rays. Conventionalscattering mechanisms can be surface roughness as disclosed in the '784patent. Certain types of scattering effects substantially depolarizelight traveling through the display. This is disadvantageous, in thatproper polarization is required for efficient LCD operation, in view ofthe typically utilized front and rear linear polarizers. Thus, each ofvolume diffusers, holographic diffusers, and reflective diffusersprovide sizes of scatter which are on the order of a wavelength of lightor smaller, and can create an undesirable depolarizing effect.

Prior art LCD diffusing systems also create parallax problems. A lightdiffuser or diffusing layer on the outside of a display's substrates, oron the outside of a display's polarizers, creates a detrimental effectcalled image parallax or pixel crosstalk. Prior art FIG. 2 illustratesthe cause of such image parallax or pixel crosstalk in an LCD. Shown inFIG. 2 are diffuser 37, 25, incident light ray 31, pixel aperture 33having a size or width "w", and pixel acceptance cone angle 35. Thedirection of incident light rays 31 striking diffuser screen 37 israndomized which increases the useful illumination cone 35 and preventsmirror images of the surrounding environment. The separation "d" ofdiffusing layer 37, 25 from pixel aperture(s) 33 allows some light 39 tocross over and exit through adjacent pixels thereby blurring theresulting image. Image parallax worsens as the separation "d" betweendiffusing layer 37 and pixel aperture(s) 33 increases because more light39 can make its way into adjacent or distant pixels. Pixel apertures 33are typically defined proximate the liquid crystal (LC) layer between orat the pixel electrodes. Thus, it would be desirable to have thediffuser as close to the LC layer as possible.

In furtherance of the above, prior art FIG. 3 illustrates a conventionaltransflective LCD configuration. The distance "d" between diffuser 37,25 and pixel aperture(s) 33 is approximately 1,100 μm. A large portionof this 1,100 μm distance "d" is defined by the thickness of glasssubstrate 17. This large separation "d" creates substantial imageparallax or pixel crosstalk due to the large distance that rays 39 cantravel laterally from their correct or originating pixel. The strongdepolarizing effect and large thickness of conventional diffusers 37, 25forces their placement as illustrated in FIG. 3 on the outside of thedisplay's substrates, and on the outside of the display's polarizers.

Prior art mass production methods of conventional diffusers are also notcompatible with placing known diffusers between glass substrates of adisplay. For example, mass production of holographic diffusers 25involves a film embossing process. The manufacturing of conventionaldiffusers requires the roughening of surfaces by physical (e.g. sanding)or chemical (e.g. etching) processes. These methods would not beefficiently utilized in providing a diffuser between either opposingpolarizers or substrates of an LCD.

It is apparent from the above that there exists a long felt need in theart for a liquid crystal display (e.g. normally white, normally black,active, TN, STN, etc.) with a diffuser layer(s) provided so as to (i)reduce image parallax or pixel crosstalk, (ii) minimize depolarizingeffects, and/or (iii) be manufacturable in mass production by way of amethod so as to be efficiently placeable in between substrates orpolarizers of a display without undue cost or sacrificing of yields. Itis a purpose of this invention to satisfy the above-described needs inthe art.

This invention will now be described with respect to certain embodimentsthereof, accompanied by certain illustrations.

SUMMARY OF THE INVENTION

Generally speaking, this invention fulfills the above-described needs inthe art by providing an LCD comprising:

first and second substantially transparent substrates;

a liquid crystal layer disposed between said first and secondsubstrates;

a light diffuser layer disposed between said liquid crystal layer andsaid second substrate, wherein said light diffuser layer includes aphoto-imageable host material portion that is substantially transparentto at least one visible wavelength of light and a plurality of diffusingparticles embedded in the host material portion; and

the host material having a refractive index of n_(h) and the diffusingparticles having a refractive index of n_(p), and wherein Δn is greaterthan or equal to about 0.05, where Δn=n_(p) -n_(h).

This invention further fulfills the above-described needs in the art byproviding a method of making an LCD, the method comprising the steps of:

providing first and second substantially transparent substrates;

providing first and second polarizers;

spin-coating a diffusing material onto the second substrate, thediffusing material including a host material which is substantiallytransparent to at least one wavelength of visible light and a pluralityof diffusing particles embedded therein;

sandwiching a liquid crystal layer between the first and secondsubstrates so that the diffusing material is located at a point betweenthe second substrate and the liquid crystal layer whereby the diffusingmaterial is positioned between the substrates; and

locating the first and second polarizers so that the resulting displayincludes the first and second substrates both located between the firstand second polarizers.

This invention will now be described with respect to certain embodimentsthereof.

IN THE DRAWINGS

FIG. 1 is a side cross-sectional view of a conventional liquid crystaldisplay with a diffuser outside of the substrates.

FIG. 2 is a schematic diagram illustrating a diffuser and correspondingpixel aperture, showing the cause of image parallax or pixel crosstalk.

FIG. 3 is a side cross-sectional view of a conventional LCD where thediffuser is located outside of the polarizers, and outside of thesubstrates.

FIG. 4 is a side cross-sectional view of a liquid crystal displayaccording to an embodiment of this invention, wherein the diffusinglayer is formed by color filters in combination with spacer beadsprovided therein, and wherein the diffuser(s) is positioned between theopposing substrates of the display.

FIG. 5 is a side cross-sectional view of a diffusing layer providedherein (e.g. from any of FIGS. 4, 6, 7, or 8), the diffusing layerincluding substantially transparent spherical balls embedded into a hostmaterial so that the refractive index of the spherical balls isdifferent than the refractive index of the host material, therebyresulting in a significant diffusing effect.

FIG. 6 is a side cross-sectional view of an LCD according to anotherembodiment of this invention, wherein a substantially continuousdiffusing layer is formed by a combination of a photoimageablesubstantially transparent host material and spacer beads disposedtherein, wherein the diffuser is positioned between the front or passivesubstrate and the color filters.

FIG. 7 is a side cross-sectional view of an LCD according to stillanother embodiment of this invention, where the diffusing layer isformed by way of a photoimageable substantially transparent hostmaterial having spacer beads disposed therein, and the diffusing layeris located between the front or passive substrate and the front pixelelectrode layer.

FIG. 8 is a side cross-sectional view of an LCD according to the FIG. 4embodiment of this invention, wherein the display includes a diffusinglayer formed by an array of photoimageable color filters having spacerbeads therein.

FIG. 9 is a plot of viewing angle versus luminance plotted on a logscale, this graph plotting a standard conventional Nitto diffuser versusa standard Fuji photoimageable red color filter versus a photoimageablered color filter having 4 μm diameter spacer beads therein.

FIG. 10 is a graph of the same data as in FIG. 9, but the luminancescale is plotted on a linear scale in fL, with FIG. 10 showing that thelarge normal incident component of the Fuji Red Color Mosaic™ filter isdiffused or spread into off normal angles by the spherical beads in thespacer inclusive embodiment.

FIG. 11 is an intensity (fL) versus vertical viewing angle graph of adisplay according to an embodiment of this invention, illustratingimproved gray scale linearity. The display configuration of FIG. 11utilized a Fuji Red Color Mosaic™ color filter including sphericaldiffusing beads therein as the diffusing layer on the viewer side andinside of the polarizers, with the liquid crystal layer beingapproximately 4.75 μm thick and the backlight being substantiallycollimated.

FIG. 12 is an intensity (fL) versus horizontal viewing angle graph ofthe display of FIG. 10, with the difference between FIG. 10 and FIG. 11being that FIG. 11 shows performance at different horizontal viewingangles along the +10° to +15° vertical viewing angle(s).

FIG. 13 is a white light contrast ratio plot of the normally whitedisplay of FIGS. 11-12, when approximately 5.85 volts were applied inthe on-state and approximately 0.47 volts in the off-state. Thethickness of the light valve LC layer was about 5.20 μm.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THIS INVENTION

Referring now more particularly to the accompanying drawings in whichlike reference numerals indicate like parts throughout the severalviews.

FIG. 4 is side cross-sectional view of layers of a transflective activematrix liquid crystal display (AMLCD) according to an embodiment of thisinvention. The display includes a plurality (or an array) of pixels,each defining a pixel aperture 33 proximate the liquid crystal layer 11.The pixel aperture size "w" is defined by the size of the correspondingpixel electrode (e.g. ITO) or the size of the opening defined by theblack matrix (whichever is smaller).

The FIG. 4 display includes, from the rear forward, conventionalsubstantially collimated backlight 41, rear linear polarizer 1, activeplate 43 which includes a rear substantially transparent glasssubstrate, an array of switching TFTs, an array of substantiallytransparent ITO (indium-tin-oxide) pixel electrodes, and a polyimide(PI) orientation layer, twisted nematic (TN) liquid crystal (LC) layer11, front polyimide orientation film 13, front common conductiveelectrode 15 (e.g. ITO), a diffusing portion 45 which in each pixel ismade up of a photoimageable color filter having diffusing spacer beadsembedded therein (an array of color filter diffusing members 45), frontsubstantially transparent glass substrate 17, and finally front linearpolarizer 19. All embodiments of this invention may be utilized inconjunction with backlit transmissive displays, backlit transflectivedisplays, and reflective displays.

The FIG. 4 display is viewed by viewer 47. Light transmitted or emittedfrom backlight 41 makes its way through rear polarizer 1 and ispolarized thereby, then it goes through active plate 43. Thereafter, thepolarized light is twisted by twisted nematic liquid crystal layer 11(when LC is in the off-state or in a semi-driven state), and thereafterthe light makes its way through each of polyimide front orientationlayer 13, and front substantially transparent common electrode 15. Thelight is then diffused by color filters 45 which also function asdiffusing members. In the FIG. 4 embodiment when each, or most of, colorfilter in the LCD function as both filters and diffusers, the layer 45is substantially transparent to some visible light (e.g. red) andsubstantially non-transparent to other visible wavelengths (e.g. blue).After being diffused, the rays proceed through substrate 17, and finallyreach front polarizer 19. Depending upon the voltage applied in eachpixel to liquid crystal layer 11, a particular amount of light from eachpixel makes its way through front polarizer 19 thereby displaying animage to viewer 47. The amount of voltage applied to LC layer 11dictates the degree to which the light polarization angle is twisted asthe light proceeds through the LC layer and the analyzer, and thus theamount of light which reaches viewer 47.

As can be seen, distance "d" between pixel aperture 33 and diffusingmember(s) 45 in the FIG. 4 display, is much less than the distance "d"between these two items in prior art FIG. 3. Thus, reduced imageparallax (or pixel crosstalk) results. Still further, diffusing layer 45is of a material which minimizes depolarizing effects, thereby allowingit to be located between the display's substrates, and also between thedisplay's polarizers 1, 19. Low depolarizing effects of diffusers inembodiments herein is achieved because of the focusing effect performedby the substantially spherical beads or particles 51. In certainembodiments, it is important that beads 51 be substantially smootharound the periphery of each bead in order to achieve efficient focusingof light to cause diffusion. Diffusing layer(s) 45 is in close proximityto pixel apertures 33 in the display (i.e. closer than the substrate17). Internal placement of diffusing layer 45 eliminates, orsubstantially reduces, image parallax effects caused by conventionaldiffusers.

Diffuser 45 has desirable properties such as being spin-coatable ontothe display, being photoimageable or photopatternable, being thin (e.g.less than about 8 μm thick, and preferably from about 4-8 μm thick),and/or having minimal or very little depolarizing effects. Thus, theinvention permits transflective LCD configurations (i) to use standardglass substrates 3, 17; (ii) diffuse light incident from the viewer sideof the display; and (iii) substantially eliminate image parallax orpixel crosstalk. Implementing this invention also significantly improvesgray scale linearity in a display.

It is noted that diffuser 45 need not be photoimageable in allembodiments of this invention. For example, diffuser may be patternableusing any type of mask, or alternatively may not be patternable at all.However, photo-imageable patternability of the diffuser layer ispreferred in certain embodiments.

The fact that diffusing layer 45 may be spin-coated (or otherwisedeposited) onto a substrate results in improved efficiency in making thedisplay. Spin-coating is compatible with other LCD production methodswhich results in improved yields and more efficient manufacturing.Furthermore, the fact that diffuser 45 is photoimageable (orphotopatternable), enables removal of unwanted material around areassuch as glue seals (this is not possible with conventional diffuserproduction methods). Still further, diffuser 45 has increasedtransmission and maintains polarization in an improved manner over priorart diffusers. By maintaining the input polarization state to a largeextent (i.e. low depolarizing properties), the result is a display whichhas contrast ratios maintained better than via conventional diffusers,when as shown in FIG. 4 the diffuser is placed between the displaysubstrates. Diffuser 45 reduces specular reflectance of a display whileincreasing the diffuse reflectance much less than conventionaldiffusers.

It is also noted that in certain embodiments of this invention (e.g. forreflective LCDs), the diffuser may be disposed on the substrate furthestfrom the viewer so that ambient light passes through the LC layer beforereaching the diffuser layer 45.

Mixing the horizontal and vertical gray scale characteristics of atwisted nematic LCD creates good gray level separation and linearity.The use of a collimated backlighting in conjunction with viewer sidediffuser 45 as shown in FIG. 4 improves gray scale linearity. Placingdiffuser 45, which is photoimageable, between the display substratessubstantially reduces or eliminates image parallax.

FIG. 5 is a side cross-sectional view of diffuser layer 45. Asillustrated, diffusing layer 45 includes a plurality of discretespherical beads 51 (or other diffusing particles) embedded in hostmaterial 53. Host material 53 is a fluid, and is compatible with knownspin-coating and photoimaging and photopatterning methods. The diametricsize of each spherical bead 51 (or the majority of beads 51) is fromabout 1 to 8 μm, preferably a diameter of from about 3-8 μm, and mostpreferably a diameter of from about 4-5 μm.

The refractive index of each spherical bead 51 is not equal to therefractive index of host material 53. This characteristic is important.According to certain embodiments of this invention, host material 53 hasa refractive index of less than about 1.45, and preferably less thanabout 1.40. In certain preferred embodiments, Nissan Chemical typeLR-201 material may be utilized for host material 53, having arefractive index of about 1.36 (at about a 550 nm wavelength) availablefrom Nissan, Japan!. Alternatively, negative resist acrylicsubstantially transparent Fuji Clear may also be used as the hostmaterial 53 (which acts as a negative resist). Meanwhile, the refractiveindex of particles or beads 51 is preferably at least about 1.5, andmost preferably from about 1.5 to 1.6. Thus, the difference inrefractive index (i.e. An) between the refractive index of host material53 and the refractive index of particles 51 is at least about 0.05, morepreferably at least about 0.1, and most preferably at least about 0.15.In certain embodiments, Δn may be within the range of from about 0.05 to0.15. This difference in refractive index (i.e. Δn) allows the beads orparticles 51 to transform the layer into a diffuser in an efficient andproductive manner.

Spherical beads 51 and host material 53 have high transmission ofvisible light, and are thus substantially transparent (preferably atleast about 90% and most preferably at least about 95%). Host material53 can alternatively absorb certain portions of the visible spectrum toproduce a color filter effect (e.g. a red color filter for example).

An example of spherical beads 51 are spacers typically used to maintainthe cell gap in liquid crystal layers of liquid crystal displays (e.g.Sekisui type MicroPearl bead spacers available from Dana Enterprises, ofCalifornia. Examples of host material 53 include photoimageable Fujicolor mosaic filter fluids (e.g. Fuji Red™) and Fuji clear (CT) coatfluids, which are used in LCD production.

Mixing beads 51 into host material 53 is done in order to achieve a highdensity of beads 51 in order to produce the diffusing layer. The mixtureof beads 51 and host material 53 is then spin-coated onto a substrate(e.g. as with normal color filters). The mixture is then photopatternedand cured thereby resulting in a diffuser (e.g. as an array of discretecolor filters/diffusers across the substrate on the passive plate). Incolor filter embodiments, because color filter is typically provided inmost, if not all, pixels in the display, this provides a non-continuousthin diffusing layer which has low back-scattering and lowdepolarization properties. Red, green, white (clear) and blue colorfilters (i.e. arrays) may be provided in such a manner, eachrepresenting a diffusing layer, across the display.

Each spherical bead 51 in a host layer functions substantially as afocusing lens. Light striking the diffusing layer 45 is focused to apoint in front of the diffusing layer and then diverges rapidly withincreasing distance, as illustrated in FIG. 5. The focusing power ofbeads 51 is a function of host material 53 refractive index n_(h), bead(or particle) 51 refractive index n_(p), and bead radius. The focusingpower (focusing power equals 1/focal length) increases with decreasingbead radius. The focusing power also increases as the index mismatch(Δn=n_(p) -n_(h)) between beads 51 and host material 53 refractive indexincreases. The diffusion profile or diffuser strength is a function ofbead density and bead focusing power. Light diffusion effect by layer 45increases as the focusing power of the spherical beads 51 increases andthe density of the beads increases. Diffusion strength can be tuned byproper selection of bead focusing power, indices of refraction, anddensity.

FIG. 8 is a side cross-sectional view of an LCD according to the FIG.4-5 embodiment of this invention, wherein color filters function as bothcolor filters and diffusing layers 45. As illustrated in FIG. 8, aplurality or an array of color filters/diffusers 45 are provided onpassive substrate 17 across the display. Preferably, a diffusinglayer/color filter 45 is provided in each pixel, although this need notbe the case in all embodiments. Red, green, and blue colorfilters/diffusers 45 are illustrated on passive substrate 17 in FIG. 8.White and other colored filters/diffuser may also be provided.

FIG. 6 is a side cross-sectional view of another embodiment of thisinvention, wherein the LCD includes diffusing layer 61 provided betweenpassive substrate 17 and color filters 65. As in the previousembodiments, diffusing layer 61 includes both host material 63 (same as53) and spheres or particles 51. Host material 63 in certain embodimentshas a dielectric constant of less than about 4.5, and acts as a negativeresist material. In this embodiment, diffusing layer 61 is separate andindependent from color filters 65, and host material is substantiallytransparent to all visible light. Diffusing layer 61 is located betweensubstrates 3 and 17, and also between polarizers 1 and 19. Specifically,diffusing layer 61 is located directly on the interior surface ofpassive substrate 17 between the substrate and color filters 65.Optionally, black matrix members 67 may also be provided on substrate 17as illustrated in FIG. 6, with diffuser 61 being located betweensubstrate 17 and black matrix members 67. Diffusing layer 61 in the FIG.6 embodiment acts and functions as discussed above relative to FIG. 5,yet it does not act as a color filter. Exemplar host materials 61 forthe FIG. 6 embodiment include photoimageable Fuji Clear™ (CT) acrylicpolymer.

FIG. 7 is a side cross-sectional view of a liquid crystal displayaccording to yet another embodiment of this invention. In the FIG. 7embodiment, color filters 65 do not act as diffusers. However, diffusinglayer 61 is provided in between substantially transparent conductivecommon electrode 15 (e.g. ITO) and color filters 65. In this embodiment,diffusing layer 61 may include a photoimageable substantiallytransparent acrylic polymer host material 63 (e.g. Fuji Clear™), withspheres 51 being as discussed above. As illustrated, diffusing layer 61in the FIG. 7 embodiment is also disposed between electrode(s) 15 andblack matrix members 67. The Δn value or difference between therefractive index n_(h) of material 63 and that n_(p) of the particles 51is as discussed above, in all embodiments of this invention.

This invention will now be described with respect to an example, whichis not intended to be limiting, of this invention. A simple prototypelight valve was built. The host material 53, 63 was Fuji color filter(red), which is photoimageable, in a 25% solids concentration. Aconcentration of 25% by weight of Micro Pearl spacer beads was added tothe Fuji host material, with the spacer beads representing spheres 51.The average diameter of each bead 51 was about 4 μm. This mixture wasthen spin-coated onto a glass substrate 17 and cured in an oven at about220° C. for approximately 30 minutes.

FIG. 9 illustrates a plot of viewing angle versus luminants plotted on alog scale, for three different samples. One of these samples (includingFuji Red™ and spacers 51) was the exemplar sample described aboveincluding the spacers. Data was collected for FIG. 9 by shining anexpanded and collimated laserbeam (632.8 nm) onto the three samples andmeasuring the output luminance as a function of angle with the Eldimtype EZContrast system. The Eldim system is described, for example, incommonly owned U.S. Ser. No. 08/876,043, filed Jun. 13, 1997, thedisclosure of which is hereby incorporated by reference. Three sampleswere measured in FIG. 9: (i) a standard Nitto diffuser, (ii) a standardFuji Red™ color filter, and (iii) the Fuji Red™ color filter with 4 μmspacer beads described above. FIG. 10 is a plot of the same data as inFIG. 9, except that the luminance scale is plotted in a linear manner.FIG. 10 illustrates that a large normal incident component of the FujiRed™ filter is diffused or spread into off normal angles by the FujiRed™ color filter plus spherical bead layer designated in solid lines.As shown in FIGS. 9-10, the addition of spherical particles 51 to hostmaterial (e.g. Fuji Red™ polymer) increases the diffusing characteristicof the resulting material, as there is higher luminance over a broaderrange of angles. While, as shown in FIGS. 9-10, the Nitto roughenedsurface diffuser had the best diffusing capability, it is notphotoimageable, not spin-coatable, cannot practically be positionedbetween a display's substrates, and has too high of a depolarizingeffect.

The polarization maintaining properties of the Fuji Red™ plus sphericalbead layer was tested and compared to the Nitto diffuser and PhysicalOptics Company holographic diffusers. The Fuji Red™ plus spherical beaddiffusing layer (e.g. FIG. 5), according to this invention, maintainedthe input polarization much better than did the conventional diffusers.The polarization test was conducted as follows: (i) the transmittedluminance of parallel polarizers was measured (two opposing polarizerswere provided with their respective linear transmission axes alignedparallel to one another); (ii) the transmitted luminance of crosspolarizers was measured (axes of opposing polarizers perpendicular toone another as in a NW TN LCD); (iii) the contrast ratio of thepolarizers in (i) and (ii) was calculated as a reference; and (iv) thisprocedure was repeated again with the Fuji Red™ 53 plus spherical beads51 inserted between the polarizers. The contrast ratio of the standardlinear polarizers alone was 3887:1. The contrast ratio of the polarizerswith Fuji Red™ plus spherical beads therebetween was 1561:1 (i.e. theextinction ratio). The contrast or extinction ratio of the Nitto samplediffuser (conventional) in between the polarizers was less than 20:1.

In certain embodiments of this invention, it is preferable that thisextinction ratio be at least about 1500:1, and is most preferably atleast about 2000:1, for any diffusing layer herein so as to minimizedepolarization effects.

The specular and diffuse reflectance of a standard Fuji Red™ colorfilter was measured and compared to that of a Fuji Red™ color filterwith spherical beads according to this invention. The specular anddiffuse reflectance of the standard Fuji Red™ color filter was,respectively, 0.46% and 0.32%. The specular and diffuse reflectance ofthe Fuji Red Color Mosaic™ color filter 53 plus beads according to thisinvention was, respectively, 0.15% and 0.61%. The measurement angle was30°. In both cases, a piece of anti-reflection coated glass was indexmatched to the sample under test. These measurements indicate that theFuji Red™ color filter plus beads according to this invention has muchlower back-scattering than a conventional diffuser. Substantiallycollimated backlights are desirable in all transflective andtransmissive embodiments herein.

FIGS. 11-12 illustrate measured display performance plots simulated inaccordance with this invention. Significant improvements in gray scalelinearity are shown. As illustrated, there is little gray scaleinversion, and there is provided excellent separation of the gray scalevoltages in the illustrated viewing zones. With regard to FIGS. 11-12,the display configuration used the Fuji Red™ color filter 53 plus beads51 discussed above as a diffusing layer on the viewer side and betweenthe polarizers. Again, the diffusing layer was spin-coated on,photopatternable, thin, and low in depolarizing effect, and thus can beinternally coated between the polarizers and between the substrates.

FIG. 13 illustrates a white light contrast ratio plot, at a plurality ofdifferent viewing angles, of the device of FIGS. 11-12.

According to the FIG. 7 embodiment of this invention, AMLCDs may be madein the following manner. Firstly, active substantially transparent glasssubstrate 3 may be provided. An array of thin film transistors (TFTs)may be formed on substrate 3 as disclosed in U.S. Pat. No. 5,641,974,the disclosure of which is incorporated herein by reference. Thereafter,on substrate 3 a photoimageable insulating layer may be provided overtop of the TFTs, with an array of discrete substantially transparentpixel electrodes 7 then being provided over the insulating layer,contacting corresponding TFTs through vias in the insulating layer, asdisclosed and described in U.S. Pat. No. 5,641,974, the disclosure ofwhich is incorporated herein by reference. A polyimide orientation film9 may then be provided over top of the array of pixel electrodes onsubstrate 3. Passive substantially transparent glass substrate 17 isalso provided. Anti-reflective black matrix portions 67 may be formedand patterned on substrate 17. Then, a layer of red color filtermaterial may be deposited on substrate 17, and thereafter patterned(e.g. using a mask and ultraviolet exposure) so as to form an array ofred color filters across substrate 17, with each red color filter tocorrespond with a red pixel. Then, a substantially continuous greencolor filter layer may be provided on substrate 17 over the black matrixportions and red color filter portions, and thereafter the green colorfilter layer being patterned so as to form an array of green colorfilters across substrate 17. An array of blue color filters is thenformed across substrate 17 in a similar manner using photoimaging. Then,a diffuser layer 61, including a plurality of spherical particles 51embedded in host material 63, may be spin-coated onto substrate 17 overtop of the color filters 65 and black matrix portion 67. The diffusinglayer may then be photoimaged using ultraviolet radiation so as to allowit to remain in a substantially continuous state across what is to bethe viewing area of the display. In TFT display embodiments, asubstantially transparent ITO layer is then deposited on substrate 17over top of diffusing layer 61, with this ITO layer then being patternedabout the edges so as to form common electrode 15. Thereafter, polyimideorientation film 13 is formed on substrate 17. It is noted thatorientation films 9 and 13 may be formed in a conventional manner, oralternatively in a multi-domain manner. Liquid crystal layer 11 is thensandwiched between substrates 3 and 17 so as to result in the displayillustrated in FIG. 7. Then, linear polarizer 1 is laminated orotherwise secured to substrate 3, while linear polarizer 19 is laminatedor otherwise secured to active substrate 17.

Once given the above disclosure, many other features, modifications, andimprovements will become apparent to the skilled artisan. Such otherfeatures, modifications, and improvements are, therefore, considered tobe a part of this invention, the scope of which is to be determined bythe following claims.

We claim:
 1. A liquid crystal display comprising:first and secondsubstantially transparent substrates; a liquid crystal layer disposedbetween said first and second substrates; a photo-imaged light diffuserlayer disposed bewteen said liquid crystal layer and said secondsubstrate, wherein said light diffuser layer includes a photo-imageablehost material portion that is substantially transparent to at least onevisible wavelength of light and a plurality of substantially sphericaldiffusing particles embedded in the host material portion; and the hostmaterial having a refractive index of n_(h) and the diffusing particleshaving a refractive index of n_(p), and wherein Δn is greater than orequal to about 0.05, where Δn=n_(p) -n_(h).
 2. The display of claim 1wherein refractive index n_(h) of the host material is less than about1.45 and refractive index n_(p) of the particles is at least about 1.5.3. The display of claim 2, wherein refractive index n_(p) is from about1.5 to 1.6, and wherein Δn is from about 0.05 to 0.15.
 4. The display ofclaim 1, wherein the host material is substantially transparent to allvisible wavelengths of light.
 5. The display of claim 1, wherein thehost material is a color filter material and is substantiallytransparent to only select wavelengths of visible light.
 6. The displayof claim 1, wherein at least a substantial number of the particles aresubstantially spherical beads, and wherein the substantially sphericalbeads have an average diametric size of from about 3 to 8 μm.
 7. Thedisplay of claim 1, further comprising color filters and a black matrixsystem disposed on said second substrate, and a backlight forilluminating the display.
 8. The display of claim 7, wherein saiddiffuser layer is located between (i) said second substrate, and (ii)said black matrix system.
 9. The display of claim 7, wherein saiddiffuser layer is located between (i) said liquid crystal layer, and(ii) said color filters and black matrix system.
 10. The display ofclaim 7, wherein said diffuser layer and said color filters are one inthe same.
 11. The display of claim 1, wherein the diffuser layer has anextinction ratio of at least about 1500:1 so as to minimizedepolarization effects.
 12. The display of claim 11, wherein thediffuser layer has an extinction ratio of at least about 2000:1.
 13. Thedisplay of claim 1, wherein the second substrate is a passive substrateand the first substrate is an active substrate including switchingdevices thereon, and wherein said second substrate is positioned betweenthe first substrate and a viewer.
 14. The display of claim 1, furthercomprising first and second linear polarizers sandwiching saidsubstrates therebetween, and wherein said host material isphoto-patternable.
 15. A liquid crystal display comprising:first andsecond substrates; a liquid crystal layer disposed between said firstand second substrates; a photo light diffuser layer disposed betweensaid liquid crystal layer and said second substrate, wherein said lightdiffuser layer includes a host material portion that is substantiallytransparent to visible wavelengths of light and a plurality ofsubstantially spherical diffusing particles embedded in the hostmaterial portion, the particles being shaped so as to focus light inorder to effect diffusing; and the host material having a refractiveindex of n_(h) and the diffusing particles having a refractive index ofn_(p), and wherein Δn is greater than or equal to about 0.05, whereΔn=n_(p) -n_(h).